JPH068490B2 - Sintered alloy with excellent specularity and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a sintered alloy produced by a powder metallurgy method and having excellent mirror surface properties, and a production method thereof.

<Prior Art> In recent years, the production of sintered parts by powder metallurgy has shown remarkable growth, and the range of application of sintered parts is expanding. Among them, the cutting method, which has a poor processing yield, is being replaced by the powder metallurgy method due to the complicated shape.

However, the sintered alloy produced by the powder metallurgy method has pores, and these pores have a drawback that the specularity and the corrosion resistance are impaired. Therefore, it is desired that the density of the sintered alloy be as high as possible.

In the conventional die press molding, the raw material powder is 200 to several 10 μm.
Since it is as large as m, the density ratio is 80 to 90% only by forming and sintering.
The porosity was also high and the pore size was coarse. In particular, since the raw material was coarse powder, coarse air holes of 50 μm or more remained between the particles, and not only specularity but also corrosion resistance was impaired. Therefore, a method of partially melting and solidifying the surface of the sintered body has been developed as a method for producing a sintered alloy having a mirror surface property.

For example, as disclosed in JP-A-62-290803, there is a method in which after sintering, the surface layer portion is melted and solidified by using a laser and then mirror-polished.

Further, in order to reduce the pores as much as possible, methods such as recompressing and re-sintering the sintered material, hot forging or hot isostatic pressing are used.

<Problems to be Solved by the Invention> However, as described above, the number of steps increases after the sintering step, which complicates the work, requires a special apparatus, and impairs the significance of the powder metallurgy method.

Further, the melting causes the surface to be deformed, which causes a problem in dimensional accuracy and the like. Therefore, such a technique of melting and solidifying and improving the surface texture must be avoided.

<Means for Solving the Problem> Then, as a result of various studies by the present inventors, the sintered body of the metal powder has a porosity of 5% (area ratio) or less, 2 μm or less.
Provided is a sintered alloy having excellent specularity, characterized in that the pores having a diameter of m or less are 60% or more, the maximum pore diameter is 10 μm or less, and the content of nonmetallic inclusions is 1% or less. To do.

The sintered alloy may have an austenitic or ferritic stainless steel composition, or Ni
It may contain 0.5 to 50% by weight and the balance Fe.

Further, in the present invention, austenitic or ferritic stainless steel powder having an average particle size of 15 μm or less and a content of non-metallic inclusions of 1% or less is used as a raw material, and a binder is added to the steel powder, After mixing and molding, the binder in the molded body is removed by heating in a non-oxidizing atmosphere, and then 1
Manufacture of a sintered alloy having excellent specularity, which is sintered at a temperature of 050 to 1350 ° C. under a reduced pressure of 0.1 Torr or less and then sintered at a temperature of 1250 to 1350 ° C. in a non-oxidizing atmosphere to polish the material. Provide a way.

The present invention further provides a metal powder having an average particle size of 15 μm or less as a raw material, and containing Ni as a main component, 0.5 to 50% by weight, and the balance Fe, and the content of nonmetallic inclusions being 1% or less. , A binder is added to the metal powder, and after mixing and molding, the binder in the molded body is removed by heating in a non-oxidizing atmosphere, followed by firing at a temperature of 1100 to 1300 ° C. in a reducing atmosphere. Provided is a method for producing a sintered alloy having excellent specularity for polishing the raw material after binding.

Hereinafter, the present invention will be described in detail.

The porosity per area has the greatest effect on the specularity, which is the main object of the present invention.

That is, as the number of pores is smaller, the specularity is improved, but it is well known that the pores remain in the sintered alloy produced by the powder metallurgy method.

In the present invention, the porosity is defined as 5% or less. When the porosity exceeds 5%, not only the total number of pores increases, but also the maximum pore diameter increases, and the shape of the pores shows a non-uniform shape from circular to angular or irregular. As a result, the specularity is lowered.

Next, in the present invention, the maximum pore diameter is defined as 10 μm or less. When the maximum pore diameter exceeds 10 μm, only the pores are preferentially polished by polishing the sintered body, and the surface becomes waviness after polishing. As a result, the reflectance is lowered and the mirror surface property is deteriorated. Inferior.

Further, in the pore distribution, 60% or more of the pores having a diameter of 2 μm or less were defined. It has been confirmed by experiments that the pores become spherical as the diameter becomes smaller, and the pores are almost spherical at 2 μm or less. Therefore, the depth from the polished surface to the bottom of the pores is 2 μm or less. The specularity depends on how light is reflected, but the specularity of the uneven surface having a depth exceeding 2 μm is deteriorated.

Furthermore, if the pores with a diameter of 2 μm or less are less than 60% of the total number of pores, the desired specularity cannot be obtained, so the lower limit is specified as such.

However, in the present invention, the pore diameter means D calculated by the following equation.

Here, S: pore cross-sectional area In addition, non-metallic inclusions that are likely to be mixed during the production of the metal powder or contained in the raw material powder itself are inevitable because the light reflectance is different from that of the metal structure. The upper limit of the existing amount was 1%. If it exceeds 1%, the desired specularity cannot be obtained. It is preferably 0.5% or less.

Next, the method for producing a sintered alloy of the present invention will be described.

The metal powder used as a raw material in the present invention is not particularly limited. For example, Fe-Ni system, stainless steel, etc. are mentioned.

When a general metal powder is used, the metal powder having an average particle size of 15 μm or less and non-metallic inclusions of 1% or less is used, a binder is mixed with the powder, and after the molding, the bonding in the molded body is performed. The agent can be obtained by heating and removing the agent in a non-oxidizing atmosphere, followed by sintering and then polishing the sintered body.

In the present invention, the metal powder having the above-mentioned component composition is mixed with an organic binder to form a molding compound.

The organic binder used here is mainly composed of thermoplastic resins, waxes, or a mixture thereof, and may further contain a plasticizer, a lubricant, a degreasing accelerator, and the like.

As the thermoplastic resin, acrylic type, polyethylene type,
One type or a mixture of two or more types such as polypropylene type and polystyrene type can be selected. As waxes, natural waxes such as beeswax, wood wax, montan wax and low molecular weight polyethylene, microcrystalline wax, paraffin, etc. One kind or two or more kinds selected from synthetic waxes represented by wax and the like can be selected and used.

The plasticizer is selected according to the combination with the main resin or wax, and is selected from di-2-ethylhexyl phthalate (DOP), di-ethyl phthalate (DEP), di-n-butyl phthalate (DHP) and the like. Can be used.

As the lubricant, higher fatty acid, fatty acid amide, fatty acid ester or the like can be used, and waxes are also used as the lubricant in some cases.

Further, a sublimable substance such as camphor can be added for the purpose of promoting degreasing.

Of course, the present invention is not limited to these organic binders, and the amount thereof also varies depending on the molding method.

As the molding machine, an extrusion molding machine, a powder rolling machine, an injection molding machine or the like is used in addition to the conventional die pressing machine.

The compounding amount of the binder is 0.5 to 3.0 in a normal die press.
The amount of the binder is about 10% by weight, but the injection molding method capable of molding a product having a complicated shape requires about 10% by weight of the binder. After molding, in order to remove the binder, the temperature is raised and maintained at a constant rate in a non-oxidizing atmosphere. If the heating rate at this time is too fast, the product will crack or swell, so the temperature is raised at 5 ° C / h to 20 ° C / h.

When the metal powder has a stainless steel composition, it contains 0.1 Torr because it contains a Cr element having a strong affinity with oxygen.
It is necessary to sinter under the following reduced pressure, but in the case of Fe-Ni alloy or the like, it is possible to sinter in a reducing atmosphere.

In the case of stainless steel, when mirror surface properties are required, it is of course necessary that the material properties also have excellent corrosion resistance. Although Cr element is most effective in improving the corrosion resistance, since the vapor pressure of Cr is high, Cr evaporates and the surface Cr concentration remarkably decreases in vacuum sintering depending on the degree of vacuum. Therefore, it is important to suppress Cr evaporation and prevent the Cr concentration distribution from becoming non-uniform. This is achieved in the present invention by vacuum sintering at low temperature followed by high temperature sintering.

Further, since it is easy to combine with oxygen, the powder surface is covered with an oxide, diffusion of atoms is blocked, and densification does not proceed easily. That is, it is necessary to reduce the Cr-based oxide, and in order to facilitate this, sintering is performed under a reduced pressure of 0.1 Torr or less.

When it exceeds 0.1 Torr, the reduction reaction of the Cr-based oxide is difficult to proceed, which is not suitable.

The temperature range of the vacuum sintering temperature is 1050 to 1350.
Since the Cr-based oxide is not sufficiently reduced at a temperature lower than 1050 ° C., the oxide remains and hinders subsequent sintering. Therefore, the lower limit is set to 1050 ° C. On the other hand, when the temperature exceeds 1350 ° C., not only the amount of evaporation from the surface of Cr becomes large and the concentration distribution becomes nonuniform, but also defects such as appearance of liquid phase and collapse of shape are observed. Therefore, the upper limit was set to 1350 ° C.

Subsequently, in order to achieve the densification and homogenization of the alloying elements by diffusion, 1250 to 1350 in a non-oxidizing atmosphere.
It is better to sinter at ° C. The low-temperature vacuum sintering in the previous stage creates contact points between the particles, and the sintering begins, but further raising the temperature promotes diffusion to promote the sintering, thereby making residual pores finer and spherical. The atmosphere is made non-oxidizing in order to suppress Cr evaporation at a high temperature of 1250 ° C. or higher.

The gases used for the non-oxidizing atmosphere are Ar and H.
e, inert gas such as N ₂ , H ₂ , CO, CH ₄ , C ₃ H
_{It is} a reducing gas such as ₈ or a combustion exhaust gas.

Sintering in the range of 1250 to 1350 ° C is 1250 ° C
At lower temperatures the density increase cannot be obtained due to the slow diffusion of the elements. When the temperature exceeds 1350 ° C, a liquid phase appears, the shape collapses, and the embrittlement phase remains, resulting in a decrease in strength. For this reason, 1250 ° C or higher, the upper limit is 1350 ° C
The following is preferable.

In the case of the Fe-Ni system, since it does not contain the non-reducing element, the sintering proceeds by using the industrially used reducing atmosphere. However, since the binder remains without being completely removed, it adversely affects the final sintered body as an impurity. For this reason, it is desirable to change to a wet hydrogen atmosphere and a dry atmosphere after holding at a dew point of 0 to 30 ° C.

The sintering temperature of the Fe—Ni system is preferably 1100 to 1300 ° C. If the temperature is lower than 1100 ° C., the diffusion rate is slow and the pore distribution that gives sufficient specularity is not exhibited, so the following is not suitable.

On the other hand, a sintering temperature of higher than 1300 ° C is economically disadvantageous because a heating element and a refractory material are heavily consumed in an industrial atmosphere sintering furnace. Furthermore, regarding the distribution of pores, no remarkable effect is observed even at a temperature exceeding that, so
It is preferably 0 ° C or lower.

Next, the sintered body obtained by the above method is polished to obtain a sintered alloy having excellent mirror surface properties. The polishing method includes barrel polishing and buff polishing, but preferably buff polishing after barrel polishing further improves the mirror surface property.

<Examples> The present invention will be specifically described below based on Examples.

(Examples 1 to 3 and Comparative Examples 1 to 3) As the raw material powder, water atomized steel powder of (SUS316 composition) having an austenitic stainless steel composition was prepared, and the average particle size was adjusted to 5.0 μm to 20 μm by classification. . A thermoplastic resin and a wax were mixed with this and kneaded using a pressure kneader. The mixing ratio at this time is 9: by weight.
It was set to 1. Using an injection molding machine, this is 40 mm long and 2 width wide.
It was molded into a rectangular parallelepiped having a thickness of 0 mm and a thickness of 3 mm. Next, the binder was removed by heating to 600 ° C. at a temperature rising rate of 10 ° C./h in a nitrogen atmosphere. In vacuum (<10 ^-3 Torr) 1150
Sintering at ℃ for 1 hour or more, and then in Ar gas atmosphere 130
Hold at 0 ° C. for 2 hours.

The surface of this sintered body was buffed and the mirror-finished surface was subjected to image processing to measure the porosity and the pore diameter. Further, the buffed surface was evaluated for specularity using a gloss meter.

Then, from the reading of the scale of the gloss meter, the specularity is A,
There are 3 levels of B and C.

A is 90% or more of the specularity of the ingot, B is 80 to 90% of the specularity of the ingot, and C is 80% or less of the specularity of the ingot.

The results are shown in Table 1.

As shown in Examples 1 to 3, the average particle size of the raw material powder is 15 μm.
m or less and pore diameter 2 μm or less is 60% or more, there are no pores of 10 μm or more, and the inclusion ratio is 1% or less, which is good. showed that.

On the other hand, Comparative Examples 1 and 2 use powder having an average particle size of 20 μm, the maximum pore size is 10 μm or more, and the porosity is 5 as well.
%, The distribution was wide and the specularity was extremely poor.

Further, in Comparative Example 3, inclusions were as high as 1.2%, and the fact that sintering was hindered also contributed to insufficient shrinkage of pores, and it is considered that the specularity of the sintered body 2 deteriorated.

(Examples 4 and 5, Comparative Examples 4 and 5) Water atomized iron powder as a raw material powder was adjusted to an average particle size of 5.0 to 18.0 μm by classification, and carbonyl N was added thereto.
2% by weight of i powder (average particle size: 8 μm) was added, and
Molded in the same manner as in ~ 3 and treated with a debinding agent. Then, it was sintered at 1250 ° C. in a hydrogen atmosphere for 2 hours. After that, the sintered body was buffed, and the porosity, pore diameter, and specularity were examined in the same manner as in Examples 1 to 3.

The results are shown in Table 2.

In each of Examples 4 and 5, the average particle size of the raw material powder was 5.0,
Since it is a fine powder of 8.0 μm, it exhibits excellent sinterability, very few residual pores are 2 μm or less, and the nonmetallic inclusions are as small as 0.1%. As a result, a sintered body having excellent specularity was obtained.

On the other hand, in Comparative Example 4, the raw material powder was a fine powder of 5.0 μm, but since the ratio of non-metallic inclusions was as high as 1.8%, it was difficult to proceed with sintering, and the pore distribution became broad. as a result,
It is considered that the sintered body became inferior in specularity.

In Comparative Example 5, since the raw material powder was as coarse as 18 μm, it was difficult to proceed with sintering, the porosity was as high as 6.4%, and a sintered body having a broad pore distribution was obtained. Further, it is considered that the specularity was lowered because the maximum pore diameter was 10 μm or more.

<Effects of the Invention> The present invention has a porosity of 5% or less, 2 μm or less pores of 60% or more, and a maximum pore diameter of 10 μm or less by ordinary solid phase sintering without performing a specific surface treatment step. It is intended to provide a sintered alloy having 1% or less of inclusions, which is suitable for mirror finishing, and a method for producing the same.

As a result, the present invention is expected to improve the yield of decorative exterior parts and the like which are required to have a mirror surface property and to expand the range of application of the parts.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Otsubo 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Division

Claims (5)

[Claims] 1. A sintered body of metal powder having a porosity of 5%.
(Area ratio) or less 60% of pores having a diameter of 2 μm or less
Above, the maximum pore diameter is 10 μm or less, and the content of non-metallic inclusions is 1% or less, a sintered alloy having excellent mirror surface properties. 2. A sintered alloy steel having excellent specularity according to claim 1, wherein the sintered alloy has an austenitic or ferritic stainless steel composition. 3. A sintered alloy steel having excellent specularity according to claim 1, wherein the sintered alloy has a composition containing Ni, 0.5 to 50% by weight, and the balance Fe. 4. An austenitic or ferritic stainless steel powder having an average particle size of 15 μm or less and a content of non-metallic inclusions of 1% or less is used as a raw material, and a binder is added to the steel powder. After mixing and molding, the binder in this molded body is removed by heating under a non-oxidizing atmosphere, followed by sintering at a temperature of 1050 to 1350 ° C. and a reduced pressure of 0.1 Torr or less, and then 1250 to 1350. ℃ temperature,
A method for producing a sintered alloy having excellent specularity, which comprises sintering the material in a non-oxidizing atmosphere and polishing the material. 5. A raw material having an average particle size of 15 μm or less,
A metal powder containing Ni, 0.5 to 50% by weight as the main component, and the balance Fe and containing 1% or less of non-metallic inclusions is used, and a binder is added to the metal powder and mixed. After molding, the binder in the molded body is removed by heating in a non-oxidizing atmosphere, and subsequently, the material is polished after sintering in a reducing atmosphere at a temperature of 1100 to 1300 ° C., and then the material is polished. Method for producing a sintered alloy having excellent properties.